A next-generation mobile communication and wireless transmission system requires an enhanced data transmission rate and an enhanced system capacity in a multi-cell environment. To satisfy such requirements, research is being conducted on an MIMO system that transmits data using a plurality of antennas, and a closed-loop MIMO system that uses channel state information for enhancing a data transmission rate in the multi-cell environment enhances transmission performance by using the channel state information.
Generally, in the MIMO system, terminals can know channel state information on a reception channel by using received data, but base stations cannot know the channel state information. Therefore, in order to enhance system performance by using the channel state information, base stations need to know the channel state information.
In a system using a closed-loop MIMO, data is transmitted by using information on respective transmission channels for terminals that receive a service from the base stations. In this case, the base stations cannot know information on respective transmission channels for the terminals that receive a service from the base stations, and thus receive channel information (for example, Channel Quality Indicator (CQI), Precoding Matrix Index (PMI), etc.) that is fed back from the terminals.
A terminal estimates a channel through which data is received, by using a signal received from a base station. The terminal calculates CQI with the estimated channel in order for the base station to apply a Modulation Coding Scheme (MCS) suitable for a channel condition when transmitting data. Also, the terminal selects a channel coefficient (i.e., a precoding vector of a codebook) most suitable for the channel condition from a priori codebook by using the estimated channel and the codebook. Channel state information, which the terminal has calculated with the estimated channel, is transmitted through a feedback channel between the base station and the terminal. The base station transmits data to the terminal by using the channel information received from the terminal, a selected MCS and the precoding vector of the codebook.
Much research is being presently conducted on the closed-loop MIMO system, and a closed-loop MIMO scheme is being applied and used even in a multi-cell environment as well as a single cell environment. However, research is inadequate on a method for reducing the influence of interference from different cells in the multi-cell environment.
Especially, a terminal located at the edge of a cell receives a weak signal from a base station for a cell in which the terminal is located, and thus, a base station for a neighbor cell experiences interference due to a terminal located in the neighbor cell. Due to this inter-cell interference, a terminal located at the edge of a cell is degraded in performance.